(a) Field of the Invention
This invention relates to a seal assembly for a rotatable shaft extending through a bore in a housing, which assembly is adapted to minimise the leakage of fluid through the bore, between the shaft and the housing. Although the seal assembly of this invention is applicable generally as a seal for a shaft rotatable within a bore in a housing, it has particular utility as a seal assembly for sealing the shaft of a turbo-charger rotor and the invention will hereinafter be described by way of example with reference to such apparatus.
(b) Description of the Prior Art
A known form of seal assembly for a shaft extending through a bore in a housing and rotatable with respect thereto, to effect a fluid seal between the shaft and the housing, comprises an annular groove formed in the shaft in the region thereof within the bore and an annular sealing member located in the groove in the shaft and bearing against the housing wall defining the bore. The sealing member may be metallic and have a radial gap at one point on the circumference thereof, whereby the ring may be expanded and contracted circumferentially to a limited extent. The `natural` or free diameter of such a ring should be slightly greater than the bore diameter, whereby the ring, when located in the groove and lying within the bore, is contracted circumferentially to a small extent, such that the ring may bear resiliently on the wall defining the bore. Such a sealing member for use in the just-described kind of seal assembly is referred to hereinafter as a "split-ring sealing member".
A seal assembly including a split-ring sealing member often is used to form a seal between a rotatable shaft and a housing therefor particularly where the shaft is to turn at a relatively high rate and hence to have a relatively high surface speed, which will preclude the use of a non-metallic resilient seal assembly, for example using a natural or synthetic rubber seal element. An example of such an application is in the case of the sealing of the rotor shaft of a turbo-charger, but due to the clearances necessary to permit the shaft to rotate and also those arising as a result of wear, the leakage of fluid--such as lubricating oil--often occurs through a seal assembly using a split-ring sealing member, particularly when the shaft is stationary.